hi,
I have 6 rx 470 nitro+ 8 Gb and all my card can do -96 mv.
For XMR 600 W for 4500 h/s in sgminer-gm so your result are not so great.
100h/card more than you isint great? My cards do -125mV, and its a really easy thing to mod in the bios, OP has stock voltage, surely you must understand what that entails. Editing the timings by hand, not that easy.
Sorry but i'm not a hater,
in your post you show this
http://virosa.ethosdistro.com/ and no card doing 850 h/s.
What i see it's your card can do 750 h/s for 1180 core and 2150 for memory.
It's good but not great.